The general objective of this study is to elucidate the mechanisms regulating progesterone production in primary pregnancy. Using the pregnant baboon as a model, the following aspects are under investigation: 1) estimation of the contributions of the placenta and ovaries to progesterone production; 2) determination of the timing of resurgence of ovarian function in pregnancy; 3) assessment of the importance of endogenous estrogens and trophic hormones on progesterone production; 4) evaluation of the relative importance of serum protein binding on progesterone metabolic clearance. BIBLIOGRAPHIC REFERENCES: Albrecht, E.D. and Townsley, J.D.: Serum Progesterone in the Pregnant Baboon (Papio papio). Biol. Reprod. 14: 610-612, 1976. Albrecht, E.D. and Townsley, J.D.: Metabolic Clearance and Production Rates of Progesterone in Nonpregnant and Pregnant Baboons (Papio papio). Endocrinology 99: 1291-1294, 1976.